Question: This North American mystery bird is often the victim of another species' breeding behaviour. What behaviour is that? What effects does this breeding behaviour have on this mystery bird species? Can you identify this mystery bird's taxonomic family and species?

Response: This is an adult male canvasback, Aythya valisineria, the largest diving duck in North America. Like all ducks, this species is placed into the taxonomic family, Anatidae, and is grouped together with the other diving ducks into the genus, Aythya.

This species gets its common name from the fine wavy pattern in its pale grey plumage, which resembles canvas. Its specific name, valisineria, is derived from the Latin for wild celery, one of their favourite foods.

The canvasback feeds primarily by digging seeds, tubers, roots, snails, and insect larvae out of the mud at the bottom of ponds. Unfortunately, they mistakenly consume lead shot as well, which causes a high mortality from lead poisoning. They also eat buds and leaves. During the 20th century, this species experienced dramatic population declines due to sharp reductions of submerged aquatic vegetation as the direct result of draining ponds and wetlands. But by the 1970s, canvasback population numbers had stabilised and scientists found that the ducks wintering the Chesapeake Bay had changed their diet: instead of eating mostly aquatic vegetation, four-fifths of these ducks' diet was made up of Baltic clams [SAV… It's What's for Dinner].

Canvasback are iconic of prairie potholes regions because they breed there, whilst wintering on ocean bays. Although they are distinctive to my eye, canvasback can be confused with redheads, although male redheads are easily distinguished by their much greyer plumage and (when you can see they entire duck), their brighter red head, smaller face and bright blue bill with a black tip. If you see redheads next to canvasback, you'll also notice they are much smaller. Female redheads are a much darker in reddish-brown colour than the pale reddish female canvasbacks.

Incubating canvasback hens are popular targets for female redhead ducks, which commonly parasitises their nests. Apparently, redheads aren't very sneaky about parasitising canvasback nests: they attack the incubating hen to force her off the nest so the redhead can add her own egg to the clutch. Since these scuffles can result in eggs being damaged, destroyed, or lost off the nest, there is a selective advantage to the canvasback not to put up much of a fight [doi:10.1093/beheco/8.2.153]. This study also found that the negative effects of brood parasitism were limited to the initial hostile act and did not affect duckling hatchability nor survivorship.

Here's a video about brood and nest parasitism of canvasback nests by redheads that you may find interesting. What I found interesting is that the narrator says the redhead intentionally rolls an egg or two out of the canvasback nest and replaces them with an egg of her own (uploaded 31 July 2009):

Interestingly, canvasback hens sometimes also lay their eggs in other canvasback nests, a behaviour known as "egg dumping". This is possibly due to two reasons: (1) these eggs act as an "insurance policy" that at least one of the parasitic female's offspring manages to survive should she lose her own nest to predators and (2) more ducklings overall mean the host's offspring are less likely to be eaten by predators.